We identified CREB3 as a novel HDAC3-interacting protein in a yeast two-hybrid screen for HDAC3-interacting proteins. Among all class I HDACs, CREB3 specifically interacts with HDAC3, in vitro and in vivo. HDAC3 efficiently inhibited CREB3-enhanced NF-κB activation, whereas the other class I HDACs did not alter NF-κB-dependent promoter activities or the expression of NF-κB target genes. Importantly, both knock-down of CREB3 and overexpression of HDAC3 suppressed the transcriptional activation of the novel CREB3-regulated gene, CXCR4. Furthermore, CREB3 was shown to bind to the CRE element in the CXCR4 promoter and to activate the transcription of the CXCR4 gene by causing dissociation of HDAC3 and subsequently increasing histone acetylation. Importantly, both the depletion of HDAC3 and the overexpression of CREB3 substantially increased the migration of MDA-MB-231 metastatic breast cancer cells. Taken together, these findings suggest that HDAC3 selectively represses CREB3-mediated transcriptional activation and chemotactic signalling in human metastatic breast cancer cells.